A 84-year-old man was admitted with dyspnea. Chest X-ray and CT showed honeycombing in the dorso-basal segments of the lung bilaterally. Idiopathic interstitial pneumonia (IIP: chronic, typical type) was diagnosed in accordance with the clinical criteria proposed by the Japanese Ministry of Health and Welfare. An extensive examination revealed no malignancy. However, the CA 19-9 level in bronchoalveolar lavage fluid (BALF) was very high (5,700 U/ml). An immunohistochemical test of lung tissue obtained by transbronchial lung biopsy was positive for CA 19-9 in bronchiolar epithelial and goblet cells. This case suggests that CA 19-9 is occasionally produced on a large scale in the lung of patients with IIP.